There were erroneous backslashes for non-dashed options (e.g \fB\option instead
of \fBoption) and missing linebreaks. Both are fixed now. Kudos got to linitian
for noticing the regressions.
The directory doc already exists and there does not seem a need to
introduces docs as an additional source of documentation.
With this change the doc layout is similar to opm-common and
opm-simulators.